This invention relates to high-speed operating mechanisms for circuit interrupters, and more specifically relates to a novel high-speed actuating mechanism using a combined lenz coil operator and pneumatic operator which can be adapted to the operation of any desired type of circuit interrupter including vacuum interrupters, gas blast interrupters, gas puffer-type interrupters and the like.
An extremely fast operating mechanism is very desirable in many circuit breaker applications. The use of a high-speed operating mechanism reduces the total interrupting time for circuit breakers and thus can minimize the length of time that an electric arc burns across the contacts and thus reduces the amount of erosion experienced by the contacts. High-speed and highly controllable operating mechanisms are also very desirable when the opening of the contacts of an interrupter should be obtained at some well-controlled predetermined time prior to current zero as in a synchronous type of circuit breaker.
It is well known that a very fast initial response can be obtained from an operating mechanism using an electrodynamic drive system consisting of a lenz coil and a movable repulsion disc coupled to the lenz coil. The movable disc is usually fixed to or is an integral part of the movable contact. These systems, however, can provide high acceleration force only for a short time since, as the gap between the disc and coil increases, the net repulsive force decreases very rapidly. To overcome this deficency, it is possible to add a mechanical assist to the system so that the opening force can be applied over a longer time. For example, it is well known to couple a pneumatic system to an electrodynamically operated system for operating a circuit interrupter as is shown in U.S. Pat. No. 3,82l,506, issued June 28, 1974, in the name of Lorne D. McConnell and assigned to the assignee of the present application.
In systems of this type, the contact itself is used as the pneumatic operating piston. This limits the pneumatic force available due to constraints imposed by the operating pressures and the contact cross-sectional area which defines the piston area. These limitations could be overcome by using a separate piston, housed in its own pressure chamber, but it then becomes very difficult to maintain proper dimensioning for appropriately locating the contact operating piston and to control seal penetration into the blast valve seal and to control the coupling between the repulsion disc and the lenz coil operator.
Moreover, in applications requiring compensation for contact erosion, as when the contacts are of the butt-type commonly used with vacuum interrupters, the placement of the separate piston in its own chamber presents complex mechanical problems.